1. Field of the Invention
The present invention relates generally to a process for testing a turbine rotor blade for a small crack, and more specifically to a process for inducing a small crack in a turbine rotor blade for use in testing for cracks.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as an aero engine used to power an aircraft, parts of the engine are often tested for cracks in order to prevent a catastrophic failure during operation. A turbine rotor blade or a rotor disk with a small crack could grow to a critical size that would result in the part breaking, and thus severe engine damage could occur with possible loss of life.
The Federal Aviation Administration (or FAA), United States Air Force (USAF), United States Navy etc. require engines to be disassembled and inspected after a certain number of hours of operation in order to determine if a part should be replaced. In the case of a turbine rotor blade, each blade in an engine is inspected for a small crack using one of several prior art testing processes. In order for the inspectors to be trained in discovering cracks, sample blades or components are cracked using prior art processes. In one such process, a turbine blade is removed from the engine and secured on a shaker table. The blade is excited by the shaker at a resonance frequency and crack detection is observed by a drop in frequency of the blade during shaking. This process often leads to the formation of large cracks in the blade. In another process, the blade is excited by a shaker at a resonance frequency and a technician uses an ocular method to observe for a crack initiation. This method does not necessarily lead to consistent results.
The FAA etc., requires inspectors to be trained and qualified on how to find a small crack in a part such as a turbine rotor blade. Various methods are used to qualify inspectors in detection of small cracks. In one such process, a florescence die is used to identify a small crack. Another includes visual observation. Inspectors are instructed on how to find small cracks by practice. However, the prior art processes for inducing a crack in a part such as a turbine blade are not very useful in that only larger cracks are produced in the part.